1. Field of the Invention
This invention relates generally to methods and apparatus for sterilizing articles, and in particular to methods and apparatus for sterilizing articles with a gas plasma generated from a gas mixture of oxidizing and reducing agents. In one particular aspect, this invention provides for the sterilization of articles with a gas plasma generated from water vapor.
A variety of sterilization methods have been proposed for sterilizing a wide range of articles such as medical products, surgical instruments, pharmaceutical products, and the like. One common method is by subjecting the articles to a gas such as ethylene oxide or other disinfecting gases. Irradiation procedures have also been proposed for sterilizing articles such as medical products.
One expectation for all sterilizing procedures is that they must effectively kill all organisms without damage to the articles or goods being sterilized. Although some sterilization procedures meet these criteria, including the use of ethylene oxide and other procedures, many sterilizers using such gases suffer from number of serious drawbacks. For example, use of such gases is often too corrosive for the articles being sterilized or their packaging materials. Another drawback is that a toxic residue usually remains on the sterilized articles. In another drawback that affects all traditional methods of sterilization, although the microorganisms are usually destroyed by the plasma, the destroyed microorganisms still physically remain on the articles.
Sterilization gas procedures and irradiation procedures often expose workers and the environment to unacceptable safety standards. Such exposure is becoming increasingly more undesirable, particularly in light of state and federal legislation restricting the use of hazardous materials.
Such restrictions are forcing hospitals and other medical facilities to search for other alternatives. One such alternative is a plasma sterilizer. Plasma sterilizers operate by injecting a gas into a chamber and applying electromagnetic radiation energy to the gas in the chamber which in turn ionizes the body of gas. The ionized gas should be highly reactive and reacts with microorganisms on the surface of the articles to be sterilized. The reactions between the ionized gas and the microorganisms should effectively destroy the microorganisms. Sterilizing plasmas have been generated with a wide variety of gases as set forth generally in U.S. Pat. No. 5,184,046, the disclosure of which is herein incorporated by reference.
One drawback with using such plasma sterilizers is that it is often difficult to ensure that all of the articles in the sterilizer have been completely sterilized. Such a problem arises because of the difficulty in achieving uniform gas dynamics and uniform plasma density when the articles being sterilized are of different sizes or shapes. This problem is compounded by the use of non-cylindrical reaction chambers and differing batch sizes. The non-uniformity of the gas dynamics results in a non-uniform plasma density, which in turn provides a non-uniform plasma treatment and insufficient sterilization.
Another problem experienced in sterilizing articles is the problem of maintaining the sterility of the articles during packaging. Current sterilization techniques, such as plasma sterilization and gas sterilization, generally require the articles to be sterilized and then subsequently packaged. To maintain sterility during packaging, the articles are packaged in a sterile environment. Such a procedure is inconvenient and expensive.
It would therefore be desirable to provide methods and apparatus to overcome or reduce such problems. In particular, the methods and apparatus should provide for plasma sterilization that is not corrosive to the articles and does not leave toxic residues on the articles. The methods and apparatus should not only be able to effectively destroy the microorganisms, but also to remove them from the articles. Further, the methods and apparatus should provide for uniform plasma distribution, thereby insuring uniform sterilization regardless of the chamber geometry or the size and geometry of the articles to be sterilized. It would further be desirable to provide methods and apparatus for sterilizing articles within packaging suitable for delivery to an end user.
2. Description of the Background Art
U.S. Pat. Nos. 5,115,166, 5,184,046, and 5,325,020 describe various apparatus and methods for plasma sterilization.
U.S. Pat. No. 4,207,286 describes a sterilization method using a continuous flow, low pressure gas plasma.